Zou, S., Bower, A., Furey, H., Susan Lozier, M., & Xu, X. (2020). Redrawing the Iceland-Scotland Overflow Water pathways in the North Atlantic. Nat Commun , 11 (1), 1890.
Abstract: Iceland-Scotland Overflow Water (ISOW) is a primary deep water mass exported from the Norwegian Sea into the North Atlantic as part of the global Meridional Overturning Circulation. ISOW has historically been depicted as flowing counter-clockwise in a deep boundary current around the subpolar North Atlantic, but this single-boundary-following pathway is being challenged by new Lagrangian observations and model simulations. We show here that ISOW leaves the boundary and spreads into the interior towards the central Labrador and Irminger basins after flowing through the Charlie-Gibbs Fracture Zone. We also describe a newly observed southward pathway of ISOW along the western flank of the Mid-Atlantic Ridge. The partitioning of these pathways is shown to be influenced by deep-reaching eddies and meanders of the North Atlantic Current. Our results, in tandem with previous studies, call for a revision in the historical depiction of ISOW pathways throughout the North Atlantic.
Xu, X., Chassignet, E. P., Johns, W. E., Schmitz Jr, W. J., & Metzger, E. J. (2014). Intraseasonal to interannual variability of the Atlantic meridional overturning circulation from eddy-resolving simulations and observations. J. Geophys. Res. Oceans , 119 (8), 5140–5159.
Zeng, L., Chassignet, E. P., Schmitt, R. W., Xu, X., & Wang, D. (2018). Salinification in the South China Sea Since Late 2012: A Reversal of the Freshening Since the 1990s. Geophys. Res. Lett. , 45 (6), 2744–2751.
Xu, X., Chassignet, E. P., Price, J. F., Özgökmen, T. M., & Peters, H. (2007). A regional modeling study of the entraining Mediterranean outflow. J. Geophys. Res. , 112 (C12).
Xu, X., Schmitz Jr., W. J., Hurlburt, H. E., Hogan, P. J., & Chassignet, E. P. (2010). Transport of Nordic Seas overflow water into and within the Irminger Sea: An eddy-resolving simulation and observations. J. Geophys. Res. , 115 (C12).
Xu, X., Bower, A., Furey, H., & Chassignet, E. P. (2018). Variability of the Iceland-Scotland Overflow Water Transport Through the Charlie-Gibbs Fracture Zone: Results From an Eddying Simulation and Observations. J. Geophys. Res. Oceans , 123 (8), 5808–5823.
Abstract: Observations show that the westward transport of the Iceland‐Scotland overflow water (ISOW) through the Charlie‐Gibbs Fracture Zone (CGFZ) is highly variable. This study examines (a) where this variability comes from and (b) how it is related to the variability of ISOW transport at upstream locations in the Iceland Basin and other ISOW flow pathways. The analyses are based on a 35‐year 1/12° eddying Atlantic simulation that represents well the main features of the observed ISOW in the area of interest, in particular, the transport variability through the CGFZ. The results show that (a) the variability of the ISOW transport is closely correlated with that of the barotropic transports in the CGFZ associated with the meridional displacement of the North Atlantic Current front and is possibly induced by fluctuations of large‐scale zonal wind stress in the Western European Basin east of the CGFZ; (b) the variability of the ISOW transport is increased by a factor of 3 from the northern part of the Iceland Basin to the CGFZ region and transport time series at these two locations are not correlated, further suggesting that the variability at the CGFZ does not come from the upstream source; and (c) the variability of the ISOW transport at the CGFZ is strongly anticorrelated to that of the southward ISOW transport along the eastern flank of the Mid‐Atlantic Ridge, suggesting an out‐of‐phase covarying transport between these two ISOW pathways.
Legg, S., Briegleb, B., Chang, Y., Chassignet, E. P., Danabasoglu, G., Ezer, T., et al. (2009). Improving Oceanic Overflow Representation in Climate Models: The Gravity Current Entrainment Climate Process Team. Bull. Amer. Meteor. Soc. , 90 (5), 657–670.
Maloney, E. D., Gettelman, A., Ming, Y., Neelin, J. D., Barrie, D., Mariotti, A., et al. (2019). Process-Oriented Evaluation of Climate and Weather Forecasting Models. Bull. Amer. Meteor. Soc. , 100 (9), 1665–1686.
Abstract: Realistic climate and weather prediction models are necessary to produce confidence in projections of future climate over many decades and predictions for days to seasons. These models must be physically justified and validated for multiple weather and climate processes. A key opportunity to accelerate model improvement is greater incorporation of process-oriented diagnostics (PODs) into standard packages that can be applied during the model development process, allowing the application of diagnostics to be repeatable across multiple model versions and used as a benchmark for model improvement. A POD characterizes a specific physical process or emergent behavior that is related to the ability to simulate an observed phenomenon. This paper describes the outcomes of activities by the Model Diagnostics Task Force (MDTF) under the NOAA Climate Program Office (CPO) Modeling, Analysis, Predictions and Projections (MAPP) program to promote development of PODs and their application to climate and weather prediction models. MDTF and modeling center perspectives on the need for expanded process-oriented diagnosis of models are presented. Multiple PODs developed by the MDTF are summarized, and an open-source software framework developed by the MDTF to aid application of PODs to centers' model development is presented in the context of other relevant community activities. The paper closes by discussing paths forward for the MDTF effort and for community process-oriented diagnosis.
Xu, X., Rhines, P. B., & Chassignet, E. P. (2016). Temperature-Salinity Structure of the North Atlantic Circulation and Associated Heat and Freshwater Transports. J. Climate , 29 (21), 7723–7742.
Xu, X., Rhines, P. B., Chassignet, E. P., & Schmitz Jr., W. J. (2015). Spreading of Denmark Strait Overflow Water in the Western Subpolar North Atlantic: Insights from Eddy-Resolving Simulations with a Passive Tracer. J. Phys. Oceanogr. , 45 (12), 2913–2932.
